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Differentiation of the Jaw Adductor Muscle of the Rosy Barb, Barbus Conchonius (Teleostei, Cyprinidae, L.), During Development
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The differentiation of the jaw adductor muscle of the rosy barb, Barbus conchonius, has been studied during development to determine the relation between fiber type and early muscle activity. First, a morphological description and a functional analysis with electromyography has been made of the jaw adductor of the adult fish. Based on this analysis and on histochemical characteristics, the jaw adductor muscle can be divided into two parts: an aerobic part, which shows contractile activity during respiration, and an anaerobic part, which is silent during respiration. Secondly, the jaw adductor muscle of embryonic and larval specimens of the barb was investigated (immuno)histochemically. From the fourth day after fertilization onwards, deeply located future-red fibers and more superficial future-white fibers can be distinguished histochemically. From the juvenile stage onwards (30 days after fertilization), the histochemical pattern of the jaw adductor is identical to that of the adult. Results are discussed in relation to the start of respiratory and feeding behaviour during development.
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Patterns of Electrophoretic and Morphologic Variability in a Widely Distributed Unionid: an Initial Survey
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Results from an initial survey of electrophoretic and morphologic variability expressed by a highly polytypic and widely distributed unionid species, Elliptio complanata, indicate that two distict races exist on the northern Atlantic Slope. The Delmarva Peninsula is a present site of introgressive hybridization between these races, and various patterns of electrophoretic and morphologic intermediacy are observed. It is proposed that this hybrid zone constitutes one of a series of contacts between geographic races of E. complanata presently distributed as a "Rassenkreis" around the Appalachian mountains. Such races were probably formed as a result of alternate phases of range expansion and contraction during Pleistocene glacial episodes, and patterns of differentiation now present among these races are consistent with initial stages of speciation as predicted by a reticulate model. Continued study of this species is likely to provide insight into patterns of transspecific change in this group of organisms.
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Host-Habitat Location and Host Location By Diachasma Alloeum Muesebeck (Hym.; Braconidae), a Parasitoid of Rhagoletis Pomonella Walsh (Dipt.; Tephritidae)
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Three laboratory experiments were designed to elucidate some of the stimuli that are involved in host micro-habitat searching, the stimulation of host-searching behaviour and in host location by Diachasma alloeum. Visual orientation was found to play an important role in the location of fruits (Crataegus mollis) by D. alloeum. Equal numbers of landings were obtained on host-infested and uninfested haws. A description is presented of the host-searching behaviour by D. alloeum on haws. It was found that probing activity and duration of stay on the fruit are strongly influenced by the presence of a Rhagoletis pomonella larva in the fruit. A quantification was made of the accuracy with which D. alloeum probes the fruit in search of hosts. It is concluded that host movement is the prime stimulus for the location of hosts. Females on haws containing a moving larva exhibited non-random probing. It was found that parasitization of the host by D. alloeum is preceeded by paralyzation of the host. When paralyzed larvae were offered in the same set-up, D. alloeum exhibited random probing.
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The Jaw Mechanism During Growth of a Generalized Haplochromis Species: H. Elegans Trewavas 1933 (Pisces, Cichlidae)
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This paper deals with the jaw mechanism of Haplochromis elegans, a generalized1 Haplochromis2 species. The central issues are the kinematics and statics of the mechanism and the way these are influenced by its proportions. These proportions change during growth and differ in related species. A mathematical computer model is formulated to deal with the kinematics and the statics of the mechanism. A calculation procedure is developed to determine the importance of the position of anatomical points in the mechanism for force-transmission during biting. It is also possible to change the position of all relevant anatomical points gradually and thereby improve the whole mechanism for the function of biting. In this way a prediction is made about the proportions expected in a powerful biting haplochromine species such as H. nigricans. The predictions made are correct in six of the seven specialized proportions of H. nigricans. A simplified kinematical model is presented which demonstrates the essence of protrusion in cichlid fishes and in many other acanthopterygian fishes. The differences in proportions of an adult and a first free-swimming stage of H. elegans are evaluated with the computer model. It appears that some proportions are more favourable for biting in the young stage, others are unfavourable due to the relative size of the eye.
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